Accelerated Death of Aerobacter aerogenes Starved in the Presence of Growth-Limiting Substrates

Abstract

Summary: Substrate-accelerated death (Postgate & Hunter, 1963a) was observed with glycerol-, glucose-, ribose-, ammonium- or phosphate-limited populations of Aerobacter aerogenes grown in defined media and starved in non-nutrient buffer; sulphate- or magnesium-limited organisms did not show this. Glucose or pyruvate accelerated death of starved populations obtained from a complex medium. Lactate-accelerated death of Escherichia coli and glucose-accelerated death of Serratia marcescens were also observed with populations of appropriate nutritional status. Glycerol-accelerated death of glycerol-limited A. aerogenes occurred with organisms from batch or continuous cultures grown at various pH values; it showed a population effect and was particularly pronounced in 0.15 m-NaCl buffered with phosphate. Continued presence of glycerol was necessary and the glycerol was metabolized. Survivors showed prolonged division lags. Tricarboxylic acid cycle intermediates, but not glucose or ribose, also accelerated death. Glycerol-accelerated death was not delayed by malonate, fluoride or fluoracetate; iodo-acetate delayed its onset but did not affect its rate; uncoupling agents antagonized it though they were themselves toxic. Glycerol-accelerated death was not accompanied by accelerated break-down of the osmotic barrier, nor by leakage of materials associated with cold shock nor by acquiring sensitivity to cold shock. No catabolism of DNA or protein accompanied it; polysaccharide was synthesized; no change in the rate of degradation of RNA was observed. Coloured substances, pyridine nucleotides, white-fluorescent material and material which absorbed at 220-230 mμ were released during glycerol-accelerated death. Magnesium ions prevented glycerol-accelerated death.